Process for desulphurizing



Patented Aug. 6, 1946 UNITED STATES PATENT OFFICE PROCESS FOR DESULPHURIZIN G HYDROCARBONS George R. Lake, Long Beach, Calif., asslgnor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application December 8, 1942, Serial No. 468,220

17 Claims.

tion.

An object of the present invention is to further the progress in preparing pure relatively sulphurfree compounds from heterogeneous hydrocarbon mixtures, using in this particular case a method and sulphur compounds.

A particular object of my invention is to separate non-aromatic hydrocarbons and sulphur aromatic hydrocarbons by dissufiiciently to permit its separation by controlled fractional distillation. Thi type of fractional distillation will be referred to hereinafter as azeotropic distillation and the substance or substances which are added to the fraction which efiect the aforementioned change will be referred to as The fractional ture results in distilling aromatic hydrocarbons and yet contains sulphur, the azeotropic distillation to remove sulphur from the remaining hydrocarbon mixture, such as one containing parafiins and olefins and naphthenes, or olefins and naphthenes or mixtures of parafiins, olefins and 65 naphthenes may be accomplished by azeotropic somewhat on the quantity of distillation in which case the distillation residue may consist of the relatively more aromatic hydrocarbons, i. e. the hydrocarbon which does not form an azeotrope with the azeotrope former or frms a higher boiling azeotrope therewith. In some cases, it may be desirable to remove only the sulphur compounds from a hydrocarbon or hydrocarbon mixture. This may also be accom plished by azeotropic distillation but in such cases it may be necessary to more carefully control the distillation to prevent substantial amounts of an azeotrope or azeotropes of the hydrocarbons from also distilling overhead in admixture with the sulphur compounds.

The type of distillation to be used depends the aze'ot'rop'e former used. I may take any proportion of the hydrocarbon fraction to the added mixture that I desire, depending on the efficiency of the operation or the purity of the product desired,-ahd the technique to be usedin the distillation. The proportion of the azeotrope former may readily be adjusted on an ideal point, the definition of this point again depending on whether I desire the portion highin aromaticity to remain as bottoms in the distillation column in a practically pure state, i. e. free from non-aromatic hydrocarbons and sulphur compounds, or whether I wish to distill'a portion of the non-aromatic hydrocarbons, leaving a portion of the non-aromatic hydrocarbons as bottoms together with aromatic hydrocarbons. Also, the distillation temperature and amount of aze'otrop'e former may be adjusted to effect the distillation of all of the non-aromatic hydrocarbons and sulphur compounds together with a portion of the aromatic hydrocarbons. In other words, the efiiciency of separation of the aromatic from nonaromatic hydrocarbons is dependent upon the proper adjustment of the amount of 'azeotro-pe former used since a small amount may result in incomplete separation of the non-aromatic hydrocarbons while the use of an excess of the azeotrop'e former together with a relatively higher distillation temperature may "cause distillation of a portion of the aromatic hydrocarbons, particularly in the case where the azeotrope former also forms an azeotrope with the aroma-tic hydrocarbons. In the foregoing separations, the sulphur compounds contained in the Stock will be distilled together with the non-aromatic hydrocarbons or if desired the azeotropic distillation may be carried out to distill overhead substantially only sulphur compounds together with azeotrope former. The latter is particularly desirable in those cases where the stock is "essentially aromatic containing only small amounts of paraflin, olefin and/or naphthene hydrocarbons. I prefer, however, to carry out the distillation so that at least a portion of the relatively less aromatic hydrocarbons will also distill overhead together with the sulphur compounds.

I have found that ketones, such as aliphatic ketones, for example, acetone, methyl ethyl ketone, diethyl ketone, methyl isopropyl ketone, diacetyl, acetonyl acetone and also the cyclic ketones, for example, cyclohexanone, methyl phenyl lieton etc., are particularly emcient in separating substantially pure aromatic hydrocarbons from complex hydrocarbon fractions of relatively narrow boiling range containing sulphur compounds. The choice-of the azeotrope former to be employed willgenerally depend upon the characteristics of the hydrocarbon stock to be treated, i. e. whether it is in the benzene,

- erable to employ an usually efficient azeotrope toluene, xylene, etc, boiling range since it is prefazeotrope former which has a boiling point of not more than 50 F. difference from the average boiling point of the hydrocarbon stock.

I have found that acetone is particularly efiicient for desulphurizing complex hydrocarbon fractions containing benzene and sulphur compounds and also non-aromatic hydrocarbons boiling between about 150 and 200 F. to produce substantially pure benzene. Acetone is an unformer for separating benzene as it does not form an azeotrope with the benzene. Substantially pure benzene is required in the production of chemical compounds or derivatives such as for producing phenols which are used in making plastics, and ethyl benzene which may be converted to styrene and employed in making synthetic rubber.

I have also found that methyl ethyl ketone, preferably containing water is an extremely efiicient azeotrope former for separating pure toluene from complex hydrocarbon fractions containing toluene, non-aromatic hydrocarbons and sulphur compounds boiling between 200 and 240 F. The production of substantially pure toluene is highly important when it is to housed in the manufacture of explosives by nitrating the toluene since small amounts of impurities seriously impair the nitration process. Since this azeotrope former does not form an azeotrope with toluene but forms an azeotrope with only the non-aromatic hydrocarbons and sulphur oompounds in the mixture, the toluene will remain as a distillation bottoms substantially free from azeotrope former.

While the foregoing description of my invention has been made with particular reference to the use of ketones for desulphurizing hydrocarbons, other azeotrope formers may be used for a this purpose, it being understood that the choice of azeotrope former for the most efficient operations will depend upon the character and boiling range of the stock undergoing treatment. Examples of such azeotrope formers include alcohols such as methyl, ethyl, propyl, butyl alcohol, fatty acids such as acetic, propionic, butyric, valeric acid, polyglycols such as mono-, di-, tri-, tetra-, hexa-, mona-ethylene glycol, propylene and di-propylene glycol, ethers and esters of such polyglycols, phenolic compounds such as phenol, resorcinol, naphthol, saturated heterocy'clic compounds of four carbon atoms such as dioxane, morpholine, di-oxolane, nitrogen bases such as picoline, pyridine, quinoline, 'rnono di-, tri-amylamine, nitroparaffins such as nitroethane, nitromethane and nitropropane.

Sulphur compounds which may be removed from hydrocarbon fractions by aze'otropic distillation, of course, include those which form azeotropes with the azeotrope former or those which in conjunction with relatively non aromatic hydrocarbons form an azeotrope with the azeotrope former. With some stock's, it is merely possible to remove by azeotropic distillation only a portion of the sulphur compounds contained in the stock, leaving a portion of the sulphur compounds in the residue together with the relatively aromatic hydrocarbons. Nevertheless, I have found that the sulphur compounds which are removable as overhead products either alone or in admixture with relatively non-aromatic hydrocarbons, together with the azeotro'pe former, are not ordinarily removable from the stock by ordinary acid treatment. I have'also found by ordinary acid treatment or extraction with solvents either in the liquid phase or vapor phase.

The reasons that certain sulphur compounds contained in stocks are removable as overhead products together with azeotrope former by azeotropic distillation while other types of sulphur compounds do not distill overhead with the azeotrope former and relatively non-aromatic hydrocarbons is not too clear. However, one explanation may be found in the fact that certain sulphur compounds such as thiophanes behave like non-aromatic hydrocarbons such as paraifins while other sulphur compounds such as thiophenes beh'ave like aromatic hydrocarbons. Thus, when a stock contains a mixture of such sulphur compounds, the sulphur compounds which behave like non-aromatic hydrocarbons are removed overhead by azeotropic distillation together with the relatively non-aromatic h'ydrocarbons, while sulphur compounds which behave like aromatic hydrocarbons remain in the residue together with the aromatic ydrocarbons. In those cases where the stock contains such mixtures of sulphur compounds, it is nevertheless possible to remove substantially all of the sulphur compounds contained in the stock by a combination of steps involving first an azeotropic distillation as described herein to remove overhead sulphur compounds either together withor without the relatively non-aromatic hydrocarbons and azeotrope former and second, an acid treatment or extraction of the residue with a solvent to remove the remaining portion of the sulphur compounds from the aromatic hydrocarbons. Selective solvent extraction processes are well known and need not be described further herein. Processes of this character are described in the McKittrick 2,162,963 and Roelfsema 2,069,329 patents. In general, the sulphur compounds which may be removed by azeotropic distillation include the th'iophanes, alkyl sulphides and perhaps mercaptans and disulphides, while those which are not separable by azeotropic distillation or remain in the aromatic residue of an azeotropic distillation process include the thiophenes and thionaphthenes.

Other objects, features and advantages of my invention will be apparent to those skilled in the art from the following examples of the invention which are not to be taken as limitin but as illustrative of my invention.

Example 1 250 parts by volume of acetone were mixed with 1000 parts by volume of a. hydrocarbon fraction obtained from coal tar having a boiling range of approximately 172 F. to 225 F. and consisting of approximately 92% benzene, 5% toluene, 1.5% sulphur. compounds and 1.5% of non-aromatic hydrocarbons such as paraffins, naphthenes and olefins. The hydrocarbon fraction had a sulphur content of 0.29% as determined by the lamp sulphur method. The mixture of acetone and hydrocarbon fraction was distilled in a fractionating column at a temperature of about 130 F. and at atmospheric pressure. This resulted in distilling overhead substantially all of the acetone and approximately 25 parts of the hydrocarbon fraction which consisted of approximately 15 parts of non-aromatic hydrocarbons and parts of sulphur compounds. This mixture was condensed and subsequently extracted with suificient water to dissolve and remove substantially all of the acetone contained therein. The 25 parts of thus extracted oil had a sulphur content of about 12%.

The undistilled bottoms of the azeotropic distillate had a sulphur content of 0.12%; This fraction was then treated with 20 pounds of 98% sulphuric acid per barrel of bottoms and then neutralized with caustic alkali which resulted in producing a fraction having 0.014%

Example 2 1000 parts of the same hydrocarbon stock described in Example 1 and having a boiling range of 172-225 F. was fractionated in a fractionating column at a temperature of about 175 P. which resulted in distilling overhead 140 parts of the hydrocarbon fraction having a sulphur content of about 1.5% and leaving about 860 parts of an undistilled bottoms having a sulphur content of about 0.10%.

The 140 parts of overhead fraction was condensed and then mixed with about parts of acetone and the mixture was distilled at a temperature of .F. and at atmospheric pressure traction with sufficient water, the fraction had a sulphur content of about 15%. The undistilled bottoms was substantially pure benzene having a sulphur content of 0.04% and amounted to about 120 parts.

The 860 parts of undistilled bottoms of the initial fractionation was distilled at a temperature of about 190 F. which resulted in distilling overhead about 800 parts of substantially pure benzene having a sulphur content of 0.04%, leaving as undistilled bottoms a fraction consisting maintropic distillation to produce about 920 parts of a benzene containing about 0.04% sulphur. blend was then treated with about 10 pounds of 98% sulphuric In order to compare the above results with ordinary acid treatment of the same stock, a portion of the same stock described above was treated with about 20 pounds of 98% sulphuric acid per barrel of stock and neutralized with caustic alkali. The thus treated product showed a sulphur content of about 0.20%.

Example 3 A portion of the same stock described in the preceding examples was fractionated to produce a benzene fraction substantially free from toluene and having a boiling range of about 172 F. to F. This fraction contained about 0.29% sulphur. 600 parts of this fraction was then mixed with 1000 parts of methanol and the mixture was distilled at a temperature of about 138 F. The distillate was separately collected in about 4% outs and each fraction was analyzed. Methanol distilled overhead with each out until all of the hydrocarbon fraction had distilled overhead,

leaving substantially pure methanol as a distillation residue. The methanol was removed from each cut by extraction with sufficient water and each hydrocarbon fraction was separately analyzed for sulphur content with the following results:

The first of distilled oil showed a sulphur content of about 2.0%; the next 5% showed a sulphur content of 0.31%, while the next 80% of distilled oil had an average sulphur content of 0.06%. The next 7% of oil had a sulphur content of 0.56% while the last 3% of oil contained 3.0% sulphur.

The foregoing experiment indicates that the stock contained at least two types of sulphur compounds, one of which was distilled overhead in the first few percent of azeotropic distillate, while the other type of sulphur compound remained as a distillation bottoms in the last 3% of oil which was subsequently distilled as an azeotrope with the methanol. These sulphur compounds could be recovered from the oil associated therewith by well known methods.

The foregoing description of my invention is not to be taken as limiting my invention but only as illustrative thereof since many variations may be made by those skilled in the art without departing from the scope of the following claims.

I claim:

1. A process for fractionating a mixture of sulphur compounds of the type contained in a coal tar fraction boiling in the benzene boiling range and comprising thiophane and thiophene which comprises distilling said mixture of sulphur compounds in the presence of a suiiicient amount of acetone adapted to form an azeotrope with thiophane thereby vaporizing that portion of said sulphur compounds comprising thiophane together with acetone and leaving the remaining portion of said sulphur compounds comprising thiophene in the residue substantially completely separated from thiophane.

2. A process for fractionating a mixture of sulphur compounds comprising thiophanes and thiophenes, which comprises distilling said mixture of sulphur compounds in the presence of a sufficient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from said mixture of sulphur compounds and adapted to form an azeotrope with said thiophanes, thereby vaporizing that portion of said sulphur compounds comprising thiophanes together with azeotrope former and leaving the remaining portion of said sulphur compounds comprising thiophenes in the residue substantially completely separated from thiophanes.

3. A process for fractionating a mixture of sulphur compounds of the type contained in a coal tar fraction boiling in the benzene boiling range and comprising thiophane, and thiophane which comprises distilling said mixture of sulphur compounds in the presence of sufficient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said mixture of sulphur compounds and adapted to form an azeotrope with thiophane, thereby vaporizing that portion of said sulphur compounds comprising thiophane together with azeotrope former and leaving the remaining portion of said sulphur compounds in the residue substantially completely separated from thiophane,

4. A process for the treatment of an aromatic hydrocarbon fraction containing amixture of sulphur compounds comprising thiophanes and thiophenes to separate thiophanes therefrom, which comprises distilling said aromatic hydrocarbon fraction in the presence of a sufiicient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said fraction to vaporize the sulphur compounds comprising thiophanes together with azeotrope former, thereby leaving aromatic hydrocarbons and thiophenes in the residue substantially completely separated from thiophanes.

5. A process for the treatment of a toluene fraction containing a mixture of sulphur compounds comprising thiophanes andthiophenes to separate thiophanes therefrom, which comprises distilling said toluene fraction in the presence of a sufficient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said fraction to vaporize the sulphur compounds comprising thiophanes together with azeotrope former, thereby leaving toluene and thiophenes in the residue substantially completely separated from said thiophanes.

6. A process for the treatment of a benzene fraction containing a mixture of sulphur compounds comprising thiophane and thiophene to separate thiophane therefrom, which comprises distilling said benzene fraction in the presence of a sufiicient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said fraction to vaporize thiophane together with azeotrope former, thereby leaving benzene and thiophane in the residue substantially completely separated from thiophane.

7. A process for the treatment of a hydrocarbon fraction containing non-aromatic hydrocarbons, aromatic hydrocarbons and a mixture of sulphur compounds comprising thiophanes and thiophenes to separate non-aromatic hydrocarbons and thiophanes from aromatic hydrocarbons and thiophenes, said non-aromatic and aromatic hydrocarbons ordinarily distilling from the hydrocarbon fraction in the same temperature range as said aromatic hydrocarbons distill therefrom, which comprises distilling said hydrocarbon fraction in the presence of a sufficient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said hydrocarbon fraction to vaporize substantially all of said non-aromatic hydrocarbons and said thiophanes together with azeotrope former, thereby leaving said aromatic hydrocarbons and said thiophenes in the residue substantially completely separated from non-aromatic hydrocarbons and thiophanes.

8. A process according to claim '7 in which said polar organic azeotrope former comprises a ketone.

9. A process for the treatment of a toluene fraction containing non-aromatic hydrocarbons and a mixture of sulphur compounds comprising thiophanes and thiophenes to separate non-aromatic hydrocarbons and thiophanes therefrom, said non-aromatic hydrocarbons and sulphur compounds ordinarily distilling from the hydrocarbon fraction in the same temperature range as said toluene distills therefrom, which comprises distilling said toluene fraction in the presence of a sufiicient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said fraction to vaporize sulphur compounds comprising thiophanes and non-aromatic hydrocarbons together with azeotrope former, thereby leaving toluene and sulphur compounds comprising thiophenes in the residue substantially completely separated from nonaromatic hydrocarbons and sulphur compounds comprising thiophanes.

10. A process according to claim 9 in which said polar organic azeotrope former is methyl ethyl ketone.

11. A process for the treatment of a benzene fraction comprising benzene, non-aromatic hydrocarbons and a mixture of sulphur compounds comprising thiophane and thiophene to separate non-aromatic hydrocarbons and thiophane therefrom, said non-aromatic hydrocarbons and sulphur compounds ordinarily distilling from the benzene fraction in the same temperature range as said benzene distills therefrom, which comprises distilling said benzene fraction in the presence of a sufilcient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said benzene fraction to vaporize thiophane and substantially all of said non-aromatic hydrocarbons together with azeotrope former, thereby leaving benzene and thiophene in the residue substantially completely separated from thiophane and non-aromatic hydrocarbons.

12. A process according to claim 11 in which said polar organic azeotrope former is acetone.

13. A process for the treatment of a hydrocarbon fraction containing non-aromatic hydrocarbons, aromatic hydrocarbons and a mixture of sulphur compounds comprising thiophanes and thiophenes to separate sulphur compounds and non-aromatic hydrocarbons from aromatic hydrocarbons contained in said hydrocarbon fraction, the non-aromatic and aromatic hydrocarbons and said sulphur compounds ordinarily all distilling from said hydrocarbon fraction in the same temperature range, which comprises distilling said hydrocarbon fraction in the presence of a sufiicient amount of a polar organic azeotrope former having a boiling point of not more than 50 F. difference from the average boiling point of said hydrocarbon fraction to vaporize substantially all of said non-aromatic hydrocarbons and the sulphur compounds comprising thiophanes together with said polar organic azeotrope former, thereby leaving said aromatic hydrocarbons in the residue substantially completely separated from said non-aroirom non-aromatic i0 matic hydrocarbons and thiophanes and coritaining a small proportion of sulphur compounds comprising thiophenes and subsequently separating said small proportion of sulphur compounds comprising thiophenes from said aromatic hydrocarbons.

14. A process according to claim 13 in which said small proportion of sulphur compounds comprising thiophenes is separated from said aromatic hydrocarbons by treatment with sulphuric acid.

15. A process according to claim 13 in which said small proportion of comprising thiophenes is aromatic hydrocarbons by extraction with a selective solvent for said thiophenes.

16. A process for producing substantially pure toluene from a hydrocarbon fraction containing toluene, non-aromatic hydrocarbons and a mixture of sulphur compounds comprising thiophanes and thiophenes, said non-aromatic hydrocarbons and mixture of sulphur compounds comprising thiophanes and thiophenes distilling in the same temperature range as toluene, which comprises distilling said hydrocarbon fraction in the presence of suificient amount of methyl ethyl ketone to vaporize substantially all of said nonaromatic hydrocarbons and said thiophanes together with methyl ethyl ketone, thereby leaving toluene in the residue substantially completely separated from non-aromatic hydrocarbons and thiophanes and containing small amounts of sulphur compounds comprising thiophenes and subsequently treating said toluene containing small amounts of sulphur compounds comprising thiophenes to separate said small amounts of sulphur compounds comprising thiophenes from said toluene.

17. A process for producing substantially pure benzene from a hydrocarbon fraction containing benzene, thiophane, thiophene and non-aromatic hydrocarbons which distill in the same temperature range as benzene, which comprises distilling said hydrocarbon fraction in the presence of acetone to vaporize substantially all of said non-aromatic hydrocarbons and said thiophane together with acetone, thereby leaving a mixture of benzene and thiophene in the residue substantially completely separated hydrocarbons and thiophane and subsequently treating said mixture of benzene and thiophene to separate said thiophene from said benzene.

GEORGE R. LAKE.

sulphur compounds separated from said 

